Pressure point for building

Politicians introduced Britain to the concept of the green belt in 1935, in response to concerns about ribbon developments rapidly rolling out from the capital towards what had once been distinct communities.

An official proposal to provide "to establish a green belt or girdle of open space" was made by the Greater London regional planning committee, and early versions were established around London, Birmingham and Sheffield.

In 1947 the Town and Country Planning Act allowed local authorities to direct development to try to hold back urban sprawl but it was not until 1955, when Conservative minister of housing Duncan Sandys issued planning circular 42/1955, that local authorities were allowed to surround cities with rings of land protected by specific planning restrictions.

Today there are 14 separate belts, varying in size from the 486,000 hectares around London to just 700 hectares at Burton-on-Trent. Greater Manchester, Merseyside, Cheshire and Lancashire have 242,000 hectares protected, and the green belt circling the cities of South and West Yorkshire totals 226,000 hectares. Wales also has its own green belt, between Cardiff and Newport, and Scotland has seven.

Green belts have five official purposes: checking unrestricted sprawl of built-up areas; preventing neighbouring towns from merging; helping safeguard the countryside from encroachment; preserving the setting and special character of historic towns; and assisting in urban regeneration.

Green belt land is by no means all rolling countryside, and new buildings can be constructed as long as they are for certain purposes, which include facilities for outdoor sport and recreation, and cemeteries.

Between 1997 and 2003 the government permitted 162 green belt developments and 2,643 acres of green belt were given up to residential use from 2000 to 2003.

Earlier this year the Social Market Foundation thinktank warned that 2m homes would have to be built on undeveloped countryside or green belt sites to meet Gordon Brown's plans to tackle the housing shortage by constructing 3m homes by 2020.